Although RFID systems offer many noteworthy characteristics, security and privacy issues associated with them are not easy to address. In this paper, the authors investigate how to solve the eavesdrop-ping, modification and one particular type of relay attacks toward the tag-to-reader communication in passive RFID systems without requiring lightweight ciphers or secret credentials shared by legitimate parties using a physical layer approach. To this end, they propose a novel physical layer scheme, called Backscatter modulation- and Uncoordinated frequency hopping-assisted Physical Layer Enhancement (BUPLE).